DeforaOS libc

About DeforaOS libc

This implementation of the standard C library has a number of goals:

• remain simple while supporting as much of POSIX as possible;
• getting rid of as much historical weight as likely;
• support any combination of kernel, compiler or hardware architecture;
• ease cross-compilation (including cross-OS) thanks to these portable headers;
• ensure code compiling with this libc will build everywhere supported as-is;
• provide a broad range of declarations for Reverse Engineering;
• generally, let headers and code be more readable to humans or programs.

Some of the most immediate benefits include faster compilation times, while also reducing the storage footprint. It is also useful during the development of programs intended to be portable across Operating Systems.

DeforaOS libc is part of the DeforaOS Project, and distributed under the terms of the BSD 2-clause license.

Compiling DeforaOS libc

Simply running make with no argument should be enough to build DeforaOS libc on your platform:

$ make

The build process uses the default compiler available on the system (through the CC variable). The compiler used can therefore be defined as follows:

$ make CC="/path/to/the/compiler"

DeforaOS libc is developed with GCC as the main compiler.

To install DeforaOS libc in a dedicated directory, like /path/to/libc:

$ make PREFIX="/path/to/libc" install

Warning: unless you know what you are doing, do not install DeforaOS libc in a directory where it might conflict with the system headers and libraries, like /usr or even the default /usr/local.

Generating Makefiles

Official releases of DeforaOS libc ship with Makefiles fitting BSD- and Linux-based platforms by default. The Makefiles are generated with configure(1) from the DeforaOS configure project, found at https://www.defora.org/os/project/16/configure.

This tool is necessary to generate Makefiles for other platforms (including macOS), or when working with development versions of DeforaOS libc.

The following command should be enough to re-generate the Makefiles:

$ configure

Please refer to the documentation of DeforaOS configure for further instructions.

Compiling programs against DeforaOS libc

The following instructions assume that DeforaOS libc is installed in the /path/to/libc directory.

With GCC:

$ make CPPFLAGS="-nostdinc -isystem /path/to/libc/include" \
  LDFLAGS="-nostdlib -L/path/to/libc/src -Wl,-rpath,/path/to/libc/src -lc /path/to/libc/src/start.o" \
  target

A specs file for GCC is also provided by DeforaOS libc, in tools/deforaos-gcc.specs. It is installed in the $PREFIX/lib/gcc directory by default. A shell wrapper for GCC using this specs file, deforaos-gcc, is also provided and installed by default.

This specs file is experimental, with some known issues remaining.

Alternatively, a pkg-config file is provided. The corresponding compilation flags can be generated as follows:

$ pkg-config --cflags DeforaOS-libc
$ pkg-config --libs DeforaOS-libc

Cross-compiling with DeforaOS libc

DeforaOS libc supports cross-compiling without any specific configuration. Simply refer to the right compiler while building, as follows:

$ make CC="/path/to/the/cross/compiler"

Compatibility with GCC's command-line syntax is assumed by default (for both building and linking).

In some cases, it is possible to build binaries cross-OS without requiring a cross-compiler in the first place. For instance, to build a Linux i386 binary on NetBSD amd64, with GCC:

Build DeforaOS libc as follows:

$ make CC="gcc -m32 -Wl,--dynamic-linker,/lib/ld-linux.so.2" \
  CPPFLAGS="-U __NetBSD__ -D __linux__"

Build the target binary as follows:

$ make CC="gcc -m32 -Wl,--dynamic-linker,/lib/ld-linux.so.2" \
  CPPFLAGS="-U __NetBSD__ -D __linux__ -nostdinc -isystem /path/to/libc/include" \
  LDFLAGS="-nostdlib -L/path/to/libc/src -Wl,-rpath,/path/to/libc/src -lc /path/to/libc/src/start.o" \
  target

This should provide a functional Linux/i386 binary.